The present invention relates to decorative synthetic resin sheets having a three-dimensional pattern and prepared by forming a foamed synthetic resin layer on one surface of a thin sheet of paper or like material which can be easily effectively adhered to surfaces of walls, ceilings or furniture, the synthetic resin layer having a three-dimensional, multicolored, embossed pattern. The invention relates also to a process for manufacturing the decorative sheets.
Decorative synthetic resin sheets must fulfill the following requirements. Decorative sheets must be readily attachable to walls or like surfaces with durable and effective bond strength. Moreover, they must have a beautiful and attractive appearance. Accordingly a three-dimensional pattern, if formed on the surface in markedly raised relief with distinctly outlined depressions and protuberances, will be aesthetically superior to a planar pattern.
Decorative synthetic resin sheets heretofore available comprise a thin synthetic resin sheet which is adapted to be adhered directly to a wall or like surface, so that they have a greatly reduced adhering ability. Especially in a cold climate, the resin sheet tends to harden to a warped state and is liable to separate from the surface. It has been desired to remedy these drawbacks.
Furthermore if it is attempted to produce a three-dimensional pattern on the surface of the decorative sheet, the pattern portion raised on the front surface will have a recess on the rear side, creating a clearance between the sheet and the surface to which it is affixed, consequently imparting an adverse effect to the adhesion of the sheet.
In order to overcome the foregoing disadvantages, a decorative sheet has been developed which is prepared by foaming a synthetic resin material containing a blowing agent and thereafter embossing the foamed sheet to create an embossed pattern on the surface. However, the embossed pattern has a very small difference (usually up to 0.8 mm) in elevation between the raised portion and the depressed portion, and it has been impossible to produce protuberances and depressions which are distinctly and sharply defined. Furthermore, it has been entirely impossible to impart different colors to the depressed bottom surface and the raised top surface respectively to produce a multi-color pattern. Consequently the decorative sheet obtained has a poor three-dimensional aesthetic effect.
Accordingly it has been suggested to employ a second embossing step following the first. The second embossing operation is conducted in exactly the same manner as in the first operation after the resin has been foamed and subsequently embossed, so that the raised pattern portion produced by the first embossing step more or less resumes the original state upon re-heating, greatly reducing the difference in elevation between the raised portion and the depressed portion. The additional operation further reduces the sharpness of the edge of the raised portion, failing to define the raised portion and depressed portion as distinguished from each other by a sharp outline. Thus, the method suggested is also unable to provide a decorative synthetic resin sheet having a highly three-dimensional effect.